Compositions containing iron, molybdenu, silicon and selected low-melting metals



United States Patent COMPOSKTIONS CONTAHNING IRON, MOLYBDE- NUM, SILICON AND SELECTED LOW-MELTHQG METALS Max F. Eechtold, Kennett Square, Pa., assignor to E. I. tlu Pont de Nemours and Company, Wilmington, Del

- a corporation of Delaware No Drawing. Filed Jan. 29, 1963, Ser. No. 254,584 Claims. (Cl. 29-1825) This invention relates to novel compositions containing iron, molybdenum, silicon, and selected low melting metals and to articles of manufacture (i.e., shaped objects) prepared therefrom.

In recent years there has developed a strong demand for structural materials capable of withstanding elevated temperatures. Such materials are employed, for example, in the fabrication of turbine blades and nozzles for jet engines, gas turbines, and the like, as Well as in high speed cutting tools and in the construction of high temperature furnaces. Examples of such structural materials are compositions containing iron, molybdenum, and silicon, described in US. Patent No. 2,866,259, which are hard and strong, creep-resistant, and resistant to oxidation even at high temperatures, e.g., up to at least 1100 C.

The ultimate object of the present invention is to provide compositions and articles of manufacture which not only have the above-noted high temperature properties of Fe-Mo-Si compositions but also have considerably lower coefficients of friction and hence are capableof sustaining higher frictional loads with less wear.

One embodiment of this invention consists of precursor compositions containing as their essential ingredients (in terms of weight percent by elemental analysis) -67% iron, 15-65% molybdenum, 857% silicon, and 525% low-melting metal(s) of the group consisting of silver, lead, tin, and combinations thereof. Other ingredients may be present provided they do not have a substantial adverse effect upon the properties desired for the articles or shaped objects of this invention. Preferably, iron, molybdenum, silicon and the low-melting metal(s) constitute at least 90% of the compositions.

Another embodiment of this invention consists of the aforesaid alloy compositions and articles or shaped objects, which are readily prepared from the precursor composiice mixture is then hot-pressed in graphite molds at a temperature of at least 950 C., preferably 1000-1300 C., and a pressure of at least 2000 p.s.i. for a period of about ten minutes to form hard shaped objects. An alternative procedure is to cold-press the powder mixture at room temperature at a pressure of at least 5000 p.s.i. and then fire the shaped object thus produced at a temperature of at least 800 0, preferably 800l300 C., in air, an inert gas or in vacuo. Heating to these temperatures should be rapid, particularly when firing is carried out in air. The shaped object can be heated with an oxygen and gas torch or by placing it in a hot furnace. Heating by induction or by direct resistance methods can likewise be employed.

Preferably an aqueous solution of an alkali metal hydroxide, e.g., NaOH of LiOH, is added to the precursor composition before it is converted to an alloy or shaped object. The alkali metal hydroxide apparently catalyzes the reaction of the components to form the objects, and in general, compositions thus treated give better results in the alpha friction test. The weight of hydroxide, which preferably is NaOH, should be between .75 and 1.5% of the weight of the metal powder.

The novel alloy compositions and objects thus produced constitute a hard silicide phase or phases through which a low-melting metal phase is dispersed, i.e., they are composed of an alloy of iron, molybdenum and silicon which contains interstitial low-melting metal(s). The metal phase (Sn, Ag, Pb, Sn-Ag, Sn-Pb, Ag-Pb, Sn-Ag-Pb) does not appear to react appreciably with the silicide within the composition ranges of this invention. X-ray examination shows that the metal is present in metallic form. Surprisingly, up to 25% of the soft metal can be tions by conventional powder metallurgy techniques and which contain the same essential ingredients.

A preferred composition for the production of alloy compositions and shaped objects contains essentially 25-31.7% Fe, 25-31.7% Mo, 25-31.7% Si, and 525% low-melting metal of the group consisting of Ag, Pb, and Sn. The thus defined composition wherein the lowmelting metal is tin is particularly preferred.

In the above compositions, the percentages given are of the total of the four essential ingredients, i.e., Fe, Mo, Si, and low-melting metal(s).

The precursor compositions, in the event they are not already composed of a homogeneous powder mixture of the desired ingredients in the form of particles less than 75 microns in size, are prepared for subsequent treatment, for example, by ball-milling powdered molybdenum, ferrosilicon, and the powdered low-melting metalconstituent until the particle size of the intimate mixture of powders is less than 75 microns. It is important that all particles be fine so that the mixture is homogeneous. The intimate tolerated without significant exudation at temperatures well above its melting point. For instance, metallic Sn is retained in the composition 28.6% l e-28.6% Mo28.-6% Sil4.3% Sn up to at least 1300 C. in air and without sacrificing the hardness or oxidation resistance of the unmodified 33.3% Fe33.3% Mo33.3% Si compositions. When silver is the low-melting metal, the high temperature stability of the compositions is particularly outsanding.

The novel alloy compositions within the scope of this invention show considerably lower coetficients of friction and bear considerably higher loads in dry alpha friction tests than do unmodified Fe-Mo-Si compositions. Generally, their coefficients of friction will be at least 20% less and their load-bearing capacity at least 25% more than for the corresponding unmodified Fe-Mo-Si alloys. Despite their lower coeflicient's of friction, the alloys and objects exhibit excellent hardness. In fact, Knoop hardness numbers, measured at g.,,for such compositions as 28.4% Fe28.6% Mo27.6% Sil4.3% Sn and 25% Fe-25% Mo25% Si25% Ag are higher than for the corresponding unmodified Fe-Mo-Si alloys.

Materials which can be used to form the precursor compositions include powdered iron, powdered molybdenum, ferrosilicon, ferromolybdenum, molybdenum-silicon, and powdered tin, silver, lead and their mixtures and alloys. Tin is the preferred soft metal because of its cost and because of the low friction surfaces it yields in combination with Fe-Mo-Si compositions. Powdered molybdenum and ferrosilicon (50% Fe) are preferred for cost and for ease of preparing the 1:1:1 ratio of FetMozSi but other combinations can be used to obtain different ratios. The commercial grades of reactants with usual impurities can be used.

The following examples illustrate the preparation and properties of the compositions and resulting shaped objects. The elemental raw materials employed in the examples, i.e., Ag, Fe, Mo, Pb, and Sn, were at least 99.7% pure. Ferrosilicons containing 4650% Fe and 47- 48.5% Si were employed, the analysis of a typical ferrosilicon being as follows: Fe, 49.62; Si, 48.23; Al, 1.10; Mn, 0.50; Ca, 0.3; Cr, 0.1; Ti, 0.1; Ni, Mg, Cu and Mo, traces. Molybdenum disilicide used in the preparation of samples 6 and 7 of Example 4 contained Mo, 62.91; Si, 35.81; others 1.28.

EXAMPLE 1 A mixture of g. of tin powder, g. of molybdenum, and g. of 50% ferrosilicon (8-20 mesh) was ballmilled (dry) for 17 hours at 85 r.p.rn. in a 250 cc. porcelain ball-mill containing cylindrical porcelain balls to yield a fine powder of input composition: 28.7% Fe- 28.9% Mo27.9% Si-l4.5% Sn. A bar was pressed from this powder at room temperature under 26,000 p.s.i. pressure and the green bar fired by placing it in an air furnace at 1300 C. It reached 1300 C. at 10 seconds and a maximum temperature above 1300 C. in 15 seconds. The following changes had occurred: (The bar was smoking slightly due to volatilization of M00 on removal.)

The resultant bar was strong, hard, and had a metallic luster.

EXAMPLE 2 A. To 12 g. of the powder prepared in Example 1 was added 2.3 g. of 5% NaOH aqueous solution; this paste was spread on glass, dried, and pulverized. The treated powder was pressed at 39,000 p.s.i. in the form of a rectangular bar with rounded corners. This bar was dried in air for 15 minutes at 105 C. and minutes at 260 C. the dried bar was fired in air for 2 minutes at 1000 C. It reached 1000 C. in 19 seconds and a maximum of about 1400 C. in 23 seconds. The following changes had occurred (no smoking was observed in removal of the bar):

Weight Thickness Width Length (s) (0211.) (cm) Green 12. 051 (37 17 1. 237 3. 85 Fired 12.080 .6081 1. 148 3. 57

The resultant strong metallic bar had a light gray surface and upon being fractured, has a tin-like appearance. The Knoop hardness numbers measured at 10 g., 100 g., and 1000 g. were 1278, 1277, and 485 respectively.

Another piece of the fired bar was subjected successively to heating in air for periods of 16 hours each at the following temperatures, with weight and measure- 1 Percentage change in weight compared to original weight. 2 Percentage change in dimension (average of three dimensions) compared to original.

Thus, after the 1000 C. heat, the sample was remarkably stable to at least 1200 C. The shrinkage at 1300 C. may indicate the onset of additional sintering. No evidence of melting or exudation was found, and little change had occurred in the appearance of the heat-treated object. Analytical determinations gave 27.95% Mo and 11.74% Sn. X-ray diffraction patterns of the heat-treated specimen showed that it was a mixture of MoSi FeSi, and ,B-Sn, and that FeSi PeSn and Fe Sn were absent. No loss in strength resulted when the specimen was held for close to a week at about C. to encourage the transformation of ,B-Sn to e-Sn. It is apparent in view of the high hardness values that the B-Sn crystals present at room temperature are very fine.

B. Hard metal bars containing 30.3% Fe, 30.3% Mo, 30.3% Si and 9.1% Pb were prepared from a mixture of 333 g. of molybdenum powder, 666 g. of ferrosilicon, and g. of lead powder using the procedure described in Example 2-A. These bars exhibited a transverse rupture strength measured at 25 C. at 29,762 p.s.i. and an impact strength of 7.2 ft. lb./sq. in.

C. An intimate mixture of 100 g. of molybdenum powder, 200 g. of ferrosilicon, and 100 g. of silver powder was cold-pressed and sintered as in Example 2-A to form hard metal bars containing 25% Fe, 25% Mo, 25% Si, and 25 Ag. The Knoop hardness numbers measured at 10 g., 100 g., and 1000 g. loads were 1548, 1222, and 685, respectively.

EXAMPLE 3 Sodium hydroxide treated powder containing 16.1% Fe, 58.1% Mo, 16.1% Si, and 9.7% Ag was prepared from a mixture of 180 g. of molybdenum powder, 100 g. of ferrosilicon, and 30 g. of silver powder using the procedure of Example 2-A. This powder was hot-pressed at 950 C. under 3000 p.s.i. for 10 minutes to form a hard metal bar. This bar exhibited a transverse rupture strength measured at 25 C. and 1000 C. of 32,600 and 42,857 p.s.i., respectively. Impact strength was 5.53 ft. lb./sq. in. and Knoop hardness numbers measured at 10 g., 100 g., and 1000 g. loads were 1752, 1411, and 762, respectively.

EXAMPLE 4 Fe-Mo-Si compositions containing Ag, Pb, or Sn were prepared by ball-milling dry, 24 to 48 hours, the ingredients listed in Table I until more than 99% passed through a 200-mesh screen. Some of these compositions were treated with 5% NaOH aqueous solution, dried and pulverized to pass 200-mesh screen. The NaOH-treated and nontreated powders were fabricated either by firing in air as in Example 2 or by hot-pressing in graphite molds as in Example 3. Details of composition and fabrication are shown in Table I.

All of these compositions were tested at r.p.m. in the dry alpha sliding friction test against hardened steel in comparison with Fe-Mo-Si compositions containing no soft metal, and other controls. The test specimens were 0.625" long, 0.250" wide and 0.400" high. The long edges were chamfered at 45 x 0.010". The surfaces tested were ground to a finish of 6-12 microinches (root mean square).

The alpha-friction test is a routine test using the Alpha Lubricant Testing Machine, Model LFW-l, manufactured by Alpha Molykote Corporation, Stamford, Connecticut. The dry friction tests were started under a load of 60 lb. for the first 2000 revolutions, after which 60 lbs. were added with each additional 360 revolutions until a frictional force of lbs. developed. The machine automatically stopped at 130 lbs. The results of these tests are summarized in Table II.

Table l PREPARATION OF TEST SPECIMENS Input Composition and Materials Fabrication Product Density Sample Fe Mo Si Other Press. Temp. Actual As Percent (p.s.i.) 0.) (g./cc.) of Theory ControlA 33. 8 33. 3 33. 8 3, 000 1, 050 4. 427 69. 4

(Fe/81+Mo) 1 1 28. 6 28. 6 14. 3 Sn 2, 000 1, 075 5. 78 89. 3

(Fe/Si+Mo+Sn) 2 1 10 Pb 3, 000 1, 050 6. 011 90. 1

(Fe/Sl-l-MO-i-Pb) 8 1 30 10 Ag 3, 000 1, 050 5. 499 82. 8

(Fe/Si+Mo+Ag) Control B 20 3,000 1, 125 5. 820 80. 4

(Fe/Si-i-Mo) 4 1 54 1 10 Pb 3,000 1, 125 6. 840 91.1

(Fe/Si-l-Mo-l-Pb) 5 1 1 54 18 10 Pb 3, 000 1, 125 6. 161 82.

(Fe/Si+Mo+Pb) 6 1 17. 1 51. 17. 14. 3 Sn 2, 000 1, 125 6. 69 92. 3

(Fe+Mo+MoSi1+Sn) 7 1 25 Sn 2, 000 1, 080 6.08 83. 9

(Fe-l-Mo-l-MoSiz-l-Sn) Control C 0 15 3, 000 1, 100 6. 881 90. 8

(Fe+Fe/Si+Mo) 8 1 28. 5 5 Pb 3, 000 1,100 6. 659 86. 4

(Fe-l-Fe/Si-l-Mo) 9 2 18 10. 14. 3 Sn 2, 000 1, 125 7. 14 ca. 95

(Fe+Fe/Si+M0+Sn) 10 3 14. 3 Sn +CP air- 1, 100 4. 55 ca. 61

(Fe+Fe/Si+Mo+Sn) fired 11 10. 14. 3 Sn *Cl? air- 1, 100 4. 60 ca. 62

(Fe-l-Fe/Si-i-M0+Sn) fired Control D 80 Cu 10 Pb 10 Sn ca. 100

(Tin Bronze, ASTM BBQ-463T) 1 Fabricated as in Example 3. 2 Fabricated as in Example 3, but without NaOH-treatment. 3 Fabricated as in Example 1. Pressed at 26,000 psi. at room temperature. Fabricated as in Example 2.

Table II ALPHA FRICTION TEST RESULTS Sample Final Load Coefficient Revolutions (lbs) of Friction Control A- 2, 721 240 542 5, 183 660 197 3, 486 360 361 3, 818 420 310 2, 745 240 542 3, 165 300 433 3, 130 300 433 3, 449 360 361 3, 110 300 433 2, 360 120 1. 083 2, 766 240 542 2, 730 240 542 2, 725 240 542 3, 812 420 310 2, 350 120 l. 083

EXAMPLE 5 A sodium hydroxide-treated powder of 15% Fe, 45% Mo, 14.5% Si, and Sn was shaped as in Example 3. The object was then subjected to the alpha friction test at 120 r.p.m. and a constant 600 lb. load while lubricated with mineral oil. The testing machine was set to stop automatically when the coeflicient of friction reached .22. After more than 363,000 revolutions, the machine was manually stopped with the coefficient of friction not yet approaching .22 and with minimum signs of wear. The steel ring gained .008 g. and the block, .0594 g. (due to oil absorption). The block scar length was 2.77 mm. This composition endured under load nine times longer than did a lubricated bronze control (80% Cir-10% Pb-10% Sn).

EXAMPLE 6 The container was pre extruded. The die was cased in tool steel, had a 1.680 inch internal diameter with /3 inch bearing land, and was of the full shear type. It was preheated to 850 F. Aluminum alloy billets 9 inches in diameter by 14 inches long with a 1.5 inch hole were preheated to 950 F. and allowed to cool to 800 F. before extruding. The die was used to extrude 26 lengths (trimmed to 94-96 ft. each) of 1.38 inch diameter pipe from these billets. Surface finish of the extruded product was excellent. Some of the extrusions were carried out at speeds in excess of 225 ft./min., well over the normal extrusion speed of -175 ft./ min. for this aluminum alloy.

The novel compositions of this invention possess low friction properties coupled with high oxidation resistance and excellent hardness at temperatures up to about 1100 C. Generally, their coefficients of friction, as measured by the dry alpha friction test, are less than 0.75. The preferred alloy compositions and objects, i.e., those containing essentially 253l.7% Fe, 2531.7% Mo, 25-31.7% Si and 5-25% low-melting metal, have coefficients of friction less than about 0.4.

Because they possess such a unique combination of properties, the alloy compositions of this invention are particularly useful for the construction dies for aluminum extrusion, where they are subjected to temperatures of 700950 F. Also, they are useful as bearing materials, particularly Where the bearings must withstand high temperatures.

It is to be understood that minor changes in the percentages of the essential ingredients will occur when the precursor compositions are converted to alloy compositions or objects due to elimination of expendable impurities in the starting materials. However, for simplicity of expression and ease of understanding, the proportions of essential ingredients in the precursor compositions and in the alloy compositions and objects have been referred to hereinabove in terms of the same numerical values.

Since obvious modifications and equivalents in the invention will be evident to those skilled in the metallurgical arts, I propose to be bound solely by the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A powder metallurgy composition consisting essentially of, by Weight, 1567% iron, 1565% molybdenum, 857% silicon, and 5-25 of a low-melting component of the group consisting of silver, lead, tin, and combinations thereof.

2. A homogeneous composition of claim 1 in the form of a powder composed of particles less than 75 microns in size.

3. A composition of claim 2 which contains between 0.75 and 1.5%, by Weight of the powder, of an alkali metal hydroxide.

4. An alloy composition consisting essentially of, by Weight, 1567% iron, 1565% molybdenum, 25-57% silicon, and 5-25% of a low-melting component of the group consisting of silver, lead, tin, and combinations thereof.

5 An article of manufacture composed of a composition of claim 4.

6. A composition of matter consisting essentially of, by weight, 2531.7% Fe, 2531.7% Mo, 25-31.7% Si,

t: and 525% of a low-melting component of the group consisting of silver, lead, and tin.

7. A composition of claim 6 wherein the low-melting component is tin.

8. A hard, strong, oxidation-resistant and creep-resistant alloy composition having a coeflicient of friction in the dry alpha friction test of less than 0.75, which consists essentially of, by weight, 15-67% iron, 15-65% molybdenum, 53-57% silicon, and 5-25% of a low-melting component of the group consisting of silver, lead, tin, and combinations thereof.

9. A shaped object composed of an alloy composition of claim 8.

10. An extrusion die composed of an alloy composition of claim 8.

References Cited in the file of this patent UNITED STATES PATENTS 1,996,220 Tigerschiold et al Apr. 2, 1935 2,866,259 Bechtold Dec. 30, 1958 3,009,309 Neri Nov. 21, 1961 

1. A POWDER METALLURGY COMPOSITION CONSISTING ESSENTIALLY OF, BY WEIGHT, 15-67% IRON, 15-65% MOLYBDENUM, 8-57% SILICON, AND 5-25% OF A LOW-MELTING COMPONENT OF THE GROUP CONSISTING OF SILVER, LEAD, TIN AND COMBINATIONS THEREOF. 